Spring loaded camming devices are used by rock climbers to help safely climb the steep walls of a natural rock surface by presenting a fall protection point which does not damage the existing rock surface.
While climbing a rock surface, a climber typically wears a safety harness which has a rope attached to it. This rope has to be connected to the rock surface at intervals as the climber progresses up the rock face such that if a fall occurs, the distance of the fall is limited due to the last connection point being fairly close by.
Historically these fall protection points were provided by devices such as bolts or pitons, which are attached to the rock either by drilling a hole and inserting a threaded fastener or by pounding a metal loop with a spike into the rock face. Either of these options permanently damages the rock face and is time consuming and requires dedicated tools.
In the 1970's another option was invented—that of the spring loaded camming device (U.S. Pat. No. 4,184,657). Spring loaded camming devices work on the principle of the logarithmic spiral—essentially a triangle wrapped around an axle providing a constantly enlarging outside diameter as the camming device is actuated allowing them to be placed into existing cracks in the rock surface. These types of devices have been in common use ever since as they require no tools to use, do not damage the existing rock face, and can easily be recovered. The devices function with opposing lobes with an outer periphery defined by a logarithmic profile which make contact with opposing rock faces and because of the geometry the contact point with the rock surface lies below the pivot point of the lobes, any applied force is translated between the rock face and the pivot point and from there to the stem of the camming device and to the rope connected to the rock climber.
For many years there were only two basic variations of the camming device—those that operated on a single axis and those that operated on two axes. The two axis models had an advantage in that they were able to encompass a wider range of openings in a single device. This was due to the pivot points being offset from each other and a larger initial radius being able to be used which allowed for a larger difference in width between ‘open’ and ‘closed’ positions, this is important because having a device with a large range of position allows for a more versatile device which means that the climber does not have to carry as many devices on their climb.
However there is a deficiency in the prior art in that the lobe axle shaft of the second axis is required to go through apertures in the lobes mounted on the first axis. Therefore, the overall lobe rotation in these devices is only approximately ninety degrees. This amount of rotation limits working distance.
In the mid 2000's, improved spring loaded camming devices were introduced which had much greater working ranges. One of these (U.S. Pat. No. 7,040,588) called the ‘link cam’ uses lobes which hinge together and unfold as the camming device is actuated. This results in a much improved range over previous devices but includes a complicated hinge mechanism which also adds significant weight.
Another device (U.S. Pat. No.: 20050037023) called the ‘super cam’ introduced at about the same time uses lobes of different sizes rotating about a common axis, the smaller of which is allowed to rotate through some 200° degrees of motion. This device also has improved range over previously existing devices, and is simpler to produce, but still does not have the range afforded by the ‘link cam’. All of the devices which have improved range also have an added weight penalty; therefore, a device with an increased range without added weight is desirable.